Preparation of sheet stock having longitudinal internal weakening therein



g- 1964 A. HANSSON ETAL PREPARATION OF SHEET STOCK HAVING LONGITUDINAL INTERNAL WEAKENING THEREIN 2 Sheets-Sheet 1 Filed Oct. 13, 1959 l8 /9 28 27 l9 l8 6 JH m 1 d m L m m N D 2 m m z )W m INVENTORS ATTORNEYS Aug. 18, 1964. g y A. HANSSON ETAL' 3,144,709

PREPARATION OF SHEET STOCK HAVING LONGITUDINAL INTERNAL WEAKENING THEREIN 2 Sheets-Sheet 2 Filed Oct. 13, 1959' United States Patent 3,144,709 PREPARATION OF SHEET STOCK HAVING 110N- GITUDINAL INTERNAL WEAKENING THEREIW Ants Hansson, Evanston, and Edward J. Ripling, Flossmoor, Ill., assignors to Continental Can Company, inc,

New York, N.Y., a corporation of New York Filed Oct. 13, 1959, Ser. No. 846,125 9 Claims. (Cl. 2Q-413) This invention relates to the preparation of sheet stock having longitudinal internal and external weakenings therein, and concerns particularly the preparation of a rolled stock having internal discontinuities and external weakenings accurately located relative to one another.

It is known to produce metallic sheet and strip stock by rolling, and to subdivide it subsequent to rolling by slitting or a like severing operation. It is also known to produce sheet material having internal discontinuities by a rolling operation which reduces the billet thickness and extends its length. The billet is provided with one or more internal channels prior to final rolling, usually when the billet is first prepared, with a content of an anti-welding or resist material which is likewise reduced in thickness and extended during the rolling, so that the resist serves to prevent welding at the discontinuity regions; wherewith the rolled strip produced is of laminate structure, comprising surface laminations of the billet metal separated by the residues of the resist material at the discontinuity regions, and with these laminations joined by integrating metal along the longitudinal edges of the billet and along longitudinal regions between adjacent discontinuity regions. When two or more such discontinuities are present, the strip is called multi-wide because it can be slit through the integrating longitudinal metal connection between resist residues and thus severed into a number of narrower strips each of which has a discontinuity therein and each of which has integrating metal connections at its edges.

The word billet is employed herein to designate a body produced as a cast ingot, or by rollor braze-bonding of slabs. Correspondingly, the word lamination is employed herein to designate a layer of the billet material which provides a surface of the strip and is separated from a cognate lamination, toward the end of the rolling schedule, by the layer of residual anti-welding material.

The rolling operation, for converting the billet to the strip, usually results in a strip having camber with one or both edges departing from straight lines; and then, when one or more internal discontinuities are present, the edges thereof are no longer straight and in the longitudinal direction of the rolling. Likewise, a widening of the stock occurs, and this widening is not uniform throughout the thickness and frequently the strip does not have parallel straight edges. Further, when an internal discontinuity is present, in practice the reduction of the original thickness of resist material may bring this to a thickness of 0.001 inch or less; and it is then difficult to discover the exact position occupied by a discontinuity in the rolled strip, and to effect longitudinal severance along lines parallel to the edges of the lamination resist residues or at right angles thereto. When a strip is rolled multi-wide, with or without internal discontinuities, it is frequently desired to be able to trim it to have parallel edges whether straight or not: and to be able to subdivide it into narrower strips with edges which are essentially parallel in each strip.

One use for such strips is in the making of tubular bodies, by employing mechanical means or fluid pressure to cause the laminations to bend away from one another. Therewith the integrating metal connections at the edges of a single-wide strip remain as externally projecting fins "ice having a thickness about twice that of the laminations, in this illustrative example. The slitting of the multiwide strip for producing the single-wide strips must be at accurately located longitudinal lines, because an intrusion of the separating slit into or too close to a discontinuity will cause cracking and leakage of the tube produced. It is feasible to have the integrating metal connections relatively wide, to permit the slitting along the same at lines safely distant from adjacent discontinuity regions, and then to trim away excess after the tube has been opened: but this represents an uneconomic loss of the metal thus trimmed away. That is, these intograting regions should be made as narrow as possible.

It has been found that the separation of a multi-Wide strip into narrower single-wide strips can be effected by providing in the multi-wide strip longitudinal line of weakening; and that such weakenings can be produced at accurately pre-selected regions by preliminary treatment of the billet during its production. This procedure is likewise effective in providing weakenings by which irregular edge portions of the strip can be detached, to provide edges which are essentially straight for strip lengths or sheets to be cut therefrom and thus provide accurate guide edges from which such cuts can be made.

One of the objects of this invention is the process of preparing a billet having longitudinal internal and surface discontinuities which become accurately positioned internal and external weakenings in the wide strip rolled from the billet and permit longitudinal severance into narrower strips having their edges accurately located relative to one another.

Another object is the process of preparing a billet by providing an open longitudinal groove on its surface, with a weld-preventing or resist material therein, and with an accurately located internal layer of resist located in a direction perpendicular to the billet surfaces, and then rolling to reduce the billet to the desired final thickness and therewith closing the groove wherewith the resist material maintains a weakening effect introduced by the said groove, and the internal resist layer provides a like weakening in alinement therewith.

A further object is the process of preparing a billet by providing longitudinal surface grooves at different spacings from its center of width, and internal layers of resist located in a direction normal to the billet surfaces, and then rolling to reduce the billet to the desired final thickness and therewith provoking a differential lateral spreading across the width as the strip is formed, where with the differential spreading compensates for and coordinates with the differential original spacing so that the groove residues in the final strip are spaced at positions determined in the billet before rolling and in alinement with the respective residues of said internal layers.

A further object is the production of a multiwide strip having a plurality of internal discontinuities spaced from one another across the width of the strip by integrating metal connecting the surface laminations at the edges of the discontinuity regions, and with internal and external weakenings accurately located at the integrating metal regions in alinement with one another at each such region and spaced from the edges of adjacent discontinuity regions.

With these and other objects in view, as will appear in the course of the following description and claims, illustrative practices are shown in the accompanying drawings, in which:

FIG. 1 is an end view of an ingot having internal and external weakening regions according to this invention, for production of a multi-wide strip;

FIG. 2 is a sectional view, on a greatly enlarged scale, of part of a multi-wide strip from the ingot of FIG. 1;

FIG. 3 is an end view of a modified billet;

FIG. 4 is a sectional view, on the scale of FIG. 2, of a multi-wide strip from the ingot of FIG. 3;

FIG. 5 is an enlarged view, showing the relative positioning of the weakenings of one set in an ingot, and the effect of initial rolling;

FIG. 6 is a corresponding view of the rolled strip, at a far greater enlargement, showing the several discontinuities therein;

FIG. 7 is an end view of a portion of a multi-wide strip, showing a detachment or severance, eg by bending operations;

FIG. 8 is a view like FIG. 7, showing detachment by a shearing or tearing operation;

FIG. 9 is a perspective view showing the tearing of a multi-wide strip and coiling of the resultant narrow strips.

In these several drawings, the parts have not been shown in their relative sizes, e.g. as stated numerically below, but thinner portions have been shown thicker to indicate the structural relationship of the parts.

An ingot may be prepared by casting a metal, e.g., steel or aluminum in a mold, to provide a body B. Incidental to the casting, or by subsequent operation thereafter, internal longitudinal channels 10 can be provided and filled with an anti-weld or resist material appropriate to the metal, the temperature to which it is subjected during the rolling schedule, and the purpose for which it is to be used. Finely powdered aluminum oxide, titanium oxide, silicon oxide, talc, graphite, and like refractories are useful with hot rolling schedules; noting that graphite should not be employed if its presence will damage the product, e.g., by electrochemical eifects or by the creation of undesirable carbide concentrations. Such an ingot may be made of a transverse dimension accepted by the rolls to be employed: and therewith may have a number of the core channels 10 spaced across its width, more than three being indicated in FIGURE 1, noting that each core channel is to provide an internal discontinuity in the multiwide final strip as a separating layer between the metal laminations of the expandable stock. The metal above and below the core channels in FIGURE 1 is integrated by metal spacers or connections 11, 12 at the longitudinal edges and between adjacent channels.

According to this invention, the ingot body B of FIG. 1 has internal longitudinal structural discontinuities 14 located between each two adjacent core channels 10 and also preferably provided between the edges of the ingot and the core channels 10 adjacent thereto. Such discontinuities 14 are to provide internal weaknesses or notches in the rolled strip, as described hereinafter. The chan nels 10 may be provided by placing flattened tubes in the ingot mold, and casting metal around them to weld thereto: in which case the abutting edges may be coated with anti-welding or resist material so that this material provides a resist film or discontinuity 14. The channels 10 can be formed in the ingot by the use of non-welding core pieces in the ingot mold, e.g. of stainless steel for aluminum or aluminum alloy ingots, or of heat-resistant metal with anti-welding coatings for steel: such core pieces can then be stretched and withdrawn from the cold ingot, and the channels filled with resist material. The channels may also be provided in filled form by employing coherent masses of anti-welding material as cores in the mold. When the channels 10 are large in dimension, they may be drilled or pierced into the solid ingots, and can be given accurate shaping by a broaching or like operation.

The discontinuities 14 can also be provided by positioning very thin resist-coated metal strips or strips of glass cloth in the mold prior to the casting. Such coatings and glass cloth disintegate and extend under the forces of the rolling operations.

The discontinuities 14 should have a dimension in the thickness direction, that is, upright in FIG. 1, which is not less than the thickness of the lamination core channels 10. For example, with a 12-inch ingot which is to be reduced to a strip 0.025 inch thick, with a residual lamination resist layer about 0.001 inch thick of a powdered resist material, the core channels 10 may be originally 0.125 to 0.500 inch thick, and the corresponding dimension of the notching discontinuity 14 can be from 5 to percent of the ingot thickness, that is, from 0.60 inch to 3.00 inches for a 12-inch ingot as shown at n in FIG. 5. The discontinuities 14 preferably have as narrow a dimension in the transverse direction or width of the ingot as can be produced and maintained: in practice the dimension can be from 0.001 to 0.010 inch, noting that this dimension does not significantly change during the rolling. The discontinuities 14 intervene between the parts of the integrating metal connectors 12.

The ingot body B of FIGURE 1 also has longitudinal external grooves 15 provided therein which are shown as of V cross-section, with each groove root in an upright plane passing through a notching discontinuity 14. In FIGURE 1, such grooves are shown at both top and bottom faces of the ingot so that a pair of grooves and a notching discontinuity are located in each upright plane as indicated by the dotted lines 16; but it will be understood that employement of only one such groove opposite each notching discontinuity 14 is comprised in the invention. Such grooves may be formed by mold wall projections, or can be later cut or impressed mechanically. The depths d, FIG. 5, of the grooves are correlated to the dimension n of the internal notching discontinuity 14. In practice the amount of metal which must be present in the initial billet at the regions where the strip later is to be notch-parted, depends upon the metal, the size of the ingot, and the rolling schedule. For example, with aluminum billets 1 /2 inches thick and 5 /2 inches wide, with several schedules of rolling to 0.018 inch total thickness, an internal discontinuity 14 to 28 percent depth, and two external grooves of 14 percent each, with 44 percent metal, the rolling occurred with a slight tendency toward splitting at the billet ends dependent upon the rolling schedule but without extension of the splitting, and a unitary strip was produced: the multi-wide laminate strips were notchparted by a single fiexure. With a 12 inch aluminum ingot, and a rolling schedule of heavy reductions without heat treatment intervening between all passes except prior to a couple final cold rollings, 6 inches of metal can be present, with 3 inches at each region In; the internal discontinuity 14 can have an original depth n of 2.4 inches; and each groove can be 1.8 inches deep. A practical minimum of percent of metal can be present for low total reduction in a number of passes; it is preferred to have to percent of the thickness occupied by metal both in the original billet and in the rolled strip.

Upon rolling the ingot of FIGURE 1, the grooves 15 are closed to give essentially smooth surfaces in the final multi-wide strip, as shown in FIGURE 2, where the metal laminae 17, 18 are separated by the residues 19 of the cores, and are connected at the edges of such lamination residues by the integrating residues 20, 21 of the connections 11, 12 of FIGURE 1. During the rolling, the metal adjacent the surfaces of the ingot is caused to flow laterally to the extent of filling the grooves 15, as shown by FIG. 5. It is preferred to coat one or both walls of each groove with an adherent layer 24 of resist or anti-welding material: and the groove walls in closing, as shown by dotted lines in FIG. 5, abut against and support the material of this layer to provide a resist-filled external weakening notch having a dimension, in the transverse direction of the billet being rolled, which is essentially determined by the thickness of the layer 24 as applied: this thickness can in practice be from 0.001 to 0.010 inch. During the early stage or stages of rolling, during which the ingot is reduced from its original thickness represented by the full lines 25 to the thickness shown by the dash lines 26, the grooves are essentially closed; therewith the major parts of the ingot are reduced in thickness by twice the amount a shown at the upper surface, FIG. 5: and therewith a proportionate reduction is accomplished at the lamination cores 10. However, due to lateral movement of metal, the depth of the grooves 15 is not reduced proportionately, but by a lesser amount b. After the grooves 15 have been closed, completion of the rolling schedule produces reductions of all parts in the direction of thickness of the ingot are essentially proportional: the billet decreases in thickness (e.g. to one five hundredths of the original) with essentially an inversely proportional increase in length (e.g. to almost 500 times the original), and with a minor increase in width.

During the course of the rolling, the over-all thickness is decreased, and therewith the ingot becomes a strip S, FIGURE 2: with an increase of width dependent upon the material and the treating and rolling schedule, and amounting to say /2 percent with a long schedule of low reductions and up to 14 percent with a schedule of very heavy reductions per pass: in practice a spread of 4 to 5 percent is an acceptable amount for an economical rolling schedule. The ingot B tends to spread more at one or more planes between the surfaces than at its top and bottom surfaces, noting that the friction between each roll and the surface contacted thereby act to restrict surface spreading. The spreading may differ at successive planes from the surfaces toward the median or central plane: e.g., when the reduction per pass is small, the spread adjacent the surfaces is greater than that at the median plane; while with high reduction per pass, the spread at the median plane is usually greater than at any plane between the median and surface planes. Therewith the residues 27 (FIG. 5) of the grooves tend to shift from positions at right angles to the surface to positions at acute angles, the angle increasing from the center of width toward the edges, as shown in FIG. 2. Dependent upon the rolling and treatment schedule, the root of each groove may or may not remain alined with the residue 28 of its associated internal notching discontinuity. When a large number of rolling passes, with low reductions each, the departure is relatively small and does not bring any groove residue at any time closer to a channel residue 19 than it is to the associated notching residue 28. Upon completion of the rolling, in each case, the distance between adjacent cores remains essentially the same as that of the connections 12 and the associated discontinuity 14 in the original billet B, e.g. 0.125 inch, while the billet thickness has been reduced to 0.025 inch for example: thus the distances between the roots of the grooves in the rolled strip S and from a groove root to the adjacent edge of the associated internal notching residue 28, are each far less than the distance from either root to the adjacent edge of a residual lamination resist residue 19.

With a 12 inch ingot having notching discontinuities 14 of the above dimensions and 0.001 inch in the direction of width of the ingot, and 45 degree V grooves of the above dimensions and with 0.010 inch coatings on one surface of each, the end of the rolling schedule on the ingot of FIG. 1 can provide a multi-wide strip as in FIG. 2, in which the metal laminations 17, 18 are each about 0.012 inch thick with a residual layer 19 about 0.001 inch thick of resist between them. In the original ingot, the spacing k, FIG. 5, between the edge of each lamination cores and the adjacent notching discontinuity 14 can be 0.062 inch, with the discontinuity 14 about .001 inch thick, so that the distance from one core 10 to the adjacent one is about 0.125 inch. Upon rolling the spacing k remains about the same; the spacing from the upper or lower edge of the notching discontinuity to the root of the adjacent groove was originally 3 inches, and is reduced to about .007 inch; the dimension in of the notching discontinuity 14 is reduced to about 0.004 inch; and the residue 27 from each groove coating now extends about 0.003 inch from the surface. That is, while the notching discontinuities 14 were closer to the lamination channels 10 in the original ingot than to the roots of the grooves 15, being 0.125 inch compared to 2 inches or 1:16, the reduction of billet thickness provides a strip in which this spacing of the notching discontinuity residues is much closer to the inner edges of the groove coating residues 27 than to the edges of the lamination residues 19, as shown in FIG. 6, being 0.005 inch compared to 0.125 inch or 25:1.

It has been found that such grooves, FIGURE 1, with an included angle of 45 degrees, are effective, when such alined grooves are formed in the upper and lower surfaces and to a depth of 15 percent of the billet thickness for each, or 30 percent in all. During the initial rolling passes, and with the metal being spread laterally to close the open groove volumes, the metal at the bottom of such grooves is not reduced proportionately to the reduction of the metal at points intermediate a pair of grooves. For example, a customary rolling procedure results in the residues of these grooves being each about 12 percent of the total thickness of the strip when reduced to final gauge, or 24 percent for the two. In general, the notches should originally have included angles less than 75 degrees, and more than about 20 degrees when spray coating thereof is employed: preferably the angle should be between 10 and 60 degrees, noting that the angles of successive grooves in a single billet may differ. Similarly, it is preferred to have the depth of each groove between 10 and 15 percent of the billet thickness, again noting that all grooves on a single billet need not have the same depth.

Such a multi-wide strip can now be separated into narrower strips as shown by FIGS. 7 to 9. In rolling, the edge of the strip may become irregular and the margins 20 can be separated from the rest or major intermediate part of the multi-wide strip, along the adjacent set of weakenings 2'7, 28, 27 at the respective edges of the strip. This provides a reference edge which is parallel to the adjacent edge of the longitudinally extending lamination resist residues 19, so that the strip can be severed transversely along lines accurately angled relative to such reference edge. The individual narrow strip can then be separated from one another along the sets of weakenings 27, 28, 27.

Such longitudinal severance can be accomplished as in FIGS. 7 and 8. Firstly, the rolled multi-wide strip S is supported at its surfaces between the pairs of arrows 35, 36 to prevent bending of the lamination region of the first narrow strip S-l. Forces are then applied alternately to the surfaces of the edge trimming piece 20 as shown by the arrows 37 so that this piece is successively moved to the dotted line positions and the metal at the region indicated by the line 16 is stressed and strained until parting occurs between the external and internal notchings 27, 28, 27, FIG. 2, and the piece 20 can be removed as shown in FIG. 8. It will be noted that the strip can be coiled, handled, stored, and shipped with the rough edged pieces 20 thereon, to avoid damage to the intervening strip material. The residual strip is then supported at surface areas, e.g. of the second narrow strip 54. between the pairs of arrows 38, 39, and bending forces applied to the first narrow strip S1, as at the arrows 35; so that the strip 5-1 is successively moved to the dotted line positions, and the stress and strain at the line 16a lead to parting thereat, so that the narrow strip S-1 can be removed, FIG. 8. This narrow strip S1 is single-wide, and has the metal laminations 17, 18 with the residual resist layer 19 between them, and with the laminations connected at their lateral edges by the integrating metal portions 21. The rest of the strip can then have successively broken lengthwise, to provide finally narrow expandable strips equal in number to the number of core channels provided in the ingot B.

In FIG. 9, the multi-wide strip S is shown as being torn into narrower sections; tearing is initiated for short distances along the lines 16, and then alternate narrow strips S-1, S3, S-5 are secured to lower coiling drums ens 1,709

Dl, D3, D and strips 8-2, 5-4, 8-6 to the upper coiling drums D-2, D-4, D6. The respective drums are secured to the driven shafts 40, 41; as the shafts turn, the strip is torn along the lines 16 and taken up as separate coils of narrow strips. The upper shaft 41 is preferably journaled on weighted, yielding supports so that it may rise as the coils increase in diameter. The edges 20 may previously be removed by tearing rolls 43, noting that this is narrow scrap material and need not be coiled for protection and storage.

When it is desired to have smoother edges on the narrow strips, rather than the minutely convex and concave edges which can result on the lateral strips with FIGS. 1 and 2, the ingot may be made as in FIG. 3, which shows one lateral half of such an ingot, as the left of the upright median plane 50. In this ingot, the internal notching channels 14 are provided as before, between adjacent lamination core channels and at the edges of the side channels. The external longitudinal grooves 15 are provided as before, with the coating layers 24 of adherent resist; but in FIG. 3, the roots of these grooves are displaced outward laterally relative to the discontinuities 14 so that the greater spreading of the ingot or billet at its center of thickness at a given rolling schedule causes a differential movement of the discontinuity and the groove root and so that at the end of rolling, the roots and the internal discontinuity of each set lie in the same upright geometrical surface as shown by the respective lines 16 in FIG. 4. The V grooves 45 are non-symmetrical, so that the groove wall surfaces have different angles relative to the billet surfaces, and with the non-symmetry increasing from the center 50 of width toward the edges of the ingot, FIG. 3, with the surface nearer the center of width having a more acute angle than the remote surface thereof. Therewith, in rolling, the residues 27 of the groove coating 24 likewise change angle during rolling due to the greater lateral spreading of the metal adjacent the groove roots than at the ingot surfaces; and with a given rolling schedule the residues 27 can come to lie essentially in the plane of the respective line 16. Thus, in the rolled strip of FIG. 4, at each notching region, the groove residues 27 and the internal notching residue 28 come to lie essentially in a plane at the respective line 16, as shown in FIG. 5 for the central notching region of the strip from the ingot of FIG. 1.

In practice, it has been found that notches of V crosssection, with the inner corners or roots having an angle of about 10 to 60 degrees, are satisfactory. Such a notch with an inner angle of 45 degrees can be coated with anti-welding material along one wall, to a thickness of 0.001 to 0.010 inch by flame spraying, by deposit and baking of a slurry of the resist material, or by powder deposit into a sharp-angled groove followed by peening the outer lips together to enclose the powder. When sharper corner angles, e.g., 8 degrees, are employed, the lateral spreading of the metal to close the groove usually causes a thickened section of the resist material to form adjacent the inner corner of the notch; grooves with inner corner or root angles of over 60 degrees are apt to leave an excessive amount of the resist on the billet surface as indicated at 29, FIG. 5, unless the resist deposit 24 has been localized and restricted to the lower part of the groove wall or steps are taken to remove the non-enclosed residue prior to completion of the rolling; whereas angles within the stated range cause the resist material to provide a weakening of substantially constant width in the direction from side to side of the rolled multi-wide strip, and often with a fairly sharp angle at its inner edge.

The lateral closure of the grooves provides smooth rolled surfaces on the multi-wide strip. For example, with a billet originally 1.50 inches thick, and having alined pairs of notches of 60 degree V section and 0.22 inch deep, no visible indentations were present on the rolled surfaces upon reduction to 0.25 inch thick. Upon rolling such billets to an over-all thickness of 0.018 inch, the

0 differential lateral spreading was found to vary with the billet material, its heat treatment before and during rolling, and the rolling schedule, that is, the number of passes and the reduction per pass.

The procedure can be employed to provide narrow marginal portions, such as 20 which may have rough or bad edges incidental to the rolling, and which can be removed to provide strip material with edges parallel to one another, and, when the internal channels are present to form a laminate stock, parallel to the adjacent edges of the channel residues and spaced therefrom by a distance predetermined by the spacing of the internal discontinuities from the internal channels. Such strip edges accurately follow any camber produced during rolling and provide reference for transverse severance and for indicating the locations of the internal channel residues.

The procedure is useful with employment of various resists at the several internal cavities, and for producing the several notchings or weakenings by the residues of such resists.

It is obvious that the illustrative practices are not restrictive, and that the invention can be employed in many ways within the scope of the appended claims.

What is claimed is:

1. The method of preparing laminate metal strip material of predetermined width for expansion into tubular form, which comprises preparing a metal billet having opposite surfaces to be engaged by the rolls during rolling, said billet having a longitudinally extending internal channel and a pair of longitudinally extending internal discontinuities, the discontinuities each having a greater dimension in the direction between said roll-engaging surfaces than the like dimension of the channel, said channel being spaced transversely from each of the discontinuities by an integral metal portion of the billet, longitudinally rolling the billet with weld-preventing material in said channel and discontinuities to cause reduction of the billet to the thickness desired for the strip material and thereby producing a smooth surfaced strip in which the dimensions of the internal weld-preventing material in the direction between the roll engaged surfaces of the billet have been coordinately reduced with the said dimensions of the residues of the discontinuities being greater than the said dimension of the residue of the channel, and then applying forces to the rolled product whereby to overstress it at and effect longitudinal separation of the metal between the rolled surfaces of the strip and the residues of the discontinuities and therewith form a narrower strip of material having a Width essentially equal to the transverse distance between the rolled residues of the discontinuities, the separated strip having metal laminations at its rolled surfaces, said laminations being separated by the rolled residue of the channel and being integrally connected at the edges by the rolled residues of the billet metal originally present between the said channel and the respective discontinuities.

2. The method of preparing laminate metal strip material for expansion into tubular form, which comprises preparing a metal billet having opposite surfaces to be engaged by the rolls during rolling, said billet having two longitudinally extending internal channels and a longitudinally extending internal discontinuity, the discontinuity having a greater dimension in the direction between said roll-engaging surfaces than the like dimension of the channels, said discontinuity being spaced transversely from each of the channels by an integral metal portion of the billet, longitudinally rolling the billet with weld-preventing material in said channel and discontinuities to cause reduction of the billet to the thickness desired for the strip material, and thereby producing a smooth surfaced strip in which the dimensions of the weld-preventing material in the direction between the roll-engaged surfaces of the billet are coordinately reduced with the said dimension of the residue of the discontinuity being greater than the said dimensions of the residues of the channels,

and then applying forces to the rolled product whereby to overstress it at and effect separation of the metal between the strip surfaces and the residue of the discontinuity and therewith form two strips of material, the individual separated strips each having metal laminations at the rolled surfaces, said laminations being separated by the rolled residue of a channel and being integrally connected at the edges by the rolled residue of a channel and being integrally connected at the edges by the rolled residues of the billet metal originally present between the said respective channel and the discontinuity.

3. The method of claim 1, in which a plurality of transversely spaced internal longitudinal channels are present, with internal longitudinal discontinuities transversely spaced from the channels, each discontinuity having a greater dimension in the direction between said roll-engaging surfaces than the like dimension of the channels, said channels being spaced transversely from each of the discontinuities by integral metal portions of the billet, and in which the rolled product is subjected to forces whereby to overstress it at and effect longitudinal separation of the metal between the rolled surfaces of the strip and the residues of the discontinuities and therewith form a plurality of narrower strips of material each having a width essentially equal to the transverse distance between two adjacent discontinuities, the separated strips each having laminations at its rolled surfaces, said laminations being separated by the rolled residue of the channel and being integrally connected at the edges by the rolled residues of the billet metal originally present between the said channel and the respective adjacent discontinuities.

4. The method of claim 1, in which external surface grooves are provided in the billet in substantial alignment with the said discontinuities, a wall of each said groove having a coating of weld-preventing material, and in which the rolling produces a strip having the residue of each internal discontinuity in essential alignment in the direction between the rolled surfaces of the strip with the rolled residue of the coating material of a respective adjacent original groove.

5. The method of claim 4, in which the distance from the said channel to the discontinuity is less in the billet than the distance from the discontinuity to the root of the groove, and during the rolling the reduction of thickness in the billet renders the distance from the weld-prevent- 10 ing residue in the discontinuity to the weld-preventing coating residue less than the distance between the residues in the said channel and said discontinuity.

6. The method of claim 4, in which longitudinal grooves are provided at both surfaces of the billet, with the groove at each surface alined with a respective internal discontinuity.

7. The method of claim 4, in which the billet has a multiplicity of pairs of grooves at each side of the center of width, and at least one of the sides of each of the grooves have successively greater angles of tilt from a plane positioned perpendicularly to the surfaces of the metal billet engaged by the rolls during rolling and passing through the root of the groove accordingly as the pair of grooves is located farther from the center of width, and in which each pair of grooves in the billet is substantially alined in the direction between the roll-contacting surfaces of the billet with a respective internal discontinuity.

8. The method of claim 1, in which the forces are applied to the rolled surfaces of rolled product at alternate regions at each side of the residue of the discontinuity and in opposite directions so that the said regions are caused to move away from one another.

9. The method of claim 1, in which the forces are applied as repeated flexings in opposite directions to effect the separation.

References Cited in the file of this patent UNITED STATES PATENTS 1,966,602 Wahlsteen July 17, 1934 2,021,945 Payne Nov. 26, 1935 2,074,712 Tross Mar. 23, 1937 2,172,767 Levine Sept. 12, 1939 2,190,494 Templin Feb. 13, 1940 2,468,206 Keene Apr. 26, 1949 2,626,457 Lieberman Jan. 27, 1953 2,690,002 Grenell Sept. 28, 1954 2,734,259 Beck Feb. 14, 1956 2,836,884 Graham June 3, 1958 2,983,994 Johnson May 16, 1961 2,986,810 Brick June 6, 1961 3,046,652 Wilkins July 31, 1962 FOREIGN PATENTS 1,145,575 France Oct. 28, 1957 

1. THE METHOD OF PREPARING LAMINATE METAL STRIP MATERIAL OF PREDETERMINED WIDTH FOR EXPANSION INTO TUBULAR FORM, WHICH COMPRISES PREPARING A METAL BILLET HAVING OPPOSITE SURFACES TO BE ENGAGED BY THE ROLLS DURING ROLLING, SAID BILLET HAVING A LONGITUDINALLY EXTENDING INTERNAL CHANNEL AND A PAIR OF LONGITUDINALLY EXTENDING INTERNAL DISCONTINUITIES, THE DISCONTINUITIES EACH HAVING A GREATER DIMENSION IN THE DIRECTION BETWEEN SAID ROLL-ENGAGING SURFACES THAN THE LIKE DIMENSION OF THE CHANNEL, SAID CHANNEL BEING SPACED TRANSVERSELY FROM EACH OF THE DISCONTINUITIES BY AN INTERGRAL METAL PORTION OF THE BILLET, LONGITUDINALLY ROLLING THE BILLET WITH WELD-PREVENTING MATERIAL IN SAID CHANNEL AND DISCONTINUITIES TO CAUSE REDUCTION OF THE BILLET TO THE THICKNESS DESIRED FOR THE STRIP MATERIAL AND THEREBY PRODUCING A SMOOTH SURFACED STRIP IN WHICH THE DIMENSIONS OF THE INTERNAL WELD-PREVENTING MATERIAL IN THE DIRECTION BETWEEN THE ROLL ENGAGED SURFACES OF THE BILLET HAVE BEEN COORDINATELY REDUCED WITH THE SAID DIMENSIONS OF THE RESIDUES OF THE DISCONTINUITIES BEING GREATER THAN THE SAID DIMENSION OF THE RESIDUE OF THE CHANNEL, AND THEN APPLYING FORCES TO THE ROLLED PRODUCT WHEREBY TO OVERSTRESS IT AT AND EFFECT LONGITUDINAL SEPARATION OF THE METAL BETWEEN THE ROLLED SURFACES OF THE STRIP AND THE RESIDUES OF THE DISCONTINUITIES AND THEREWITH FROM A NARROWER STRIP OF MATERIAL HAVING A WIDTH ESSENTIALLY EQUAL TO THE TRANSVERSE DISTANCE BETWEEN THE ROLLED RESIDUES OF THE DICONTINUITIES, THE SEPARATED STRIP HAVING METAL LAMINATIONS AT ITS ROLLED SURFACES, SAID LAMINATIONS BEING SEPARATED BY THE ROLLED RESIDUE OF THE CHANNEL AND BEING INTEGRALLY CONNECTED AT THE EDGES BY THE ROLLED RESIDUES OF THE BILLET METAL ORIGINALLY PRESENT BETWEEN THE SAID CHANNEL AND THE RESPECTIVE DISCONTINNUITIES. 